[Qemu-devel] [PATCH v5 1/7] docs: update documentation for memory hot unplug

[Zhu Guihua]

Add specification about how to use memory hot unplug, and add
a flow diagram to explain memory hot unplug process.

Signed-off-by: Zhu Guihua <address@hidden>
---
 docs/memory-hotplug.txt         | 24 ++++++++++++++++++++----
 docs/specs/acpi_mem_hotplug.txt | 16 +++++++++++++++-
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/docs/memory-hotplug.txt b/docs/memory-hotplug.txt
index f70571d..0de7f1b 100644
--- a/docs/memory-hotplug.txt
+++ b/docs/memory-hotplug.txt
@@ -1,12 +1,10 @@
 QEMU memory hotplug
 ===================
 
-This document explains how to use the memory hotplug feature in QEMU,
+This part explains how to use the memory hotplug feature in QEMU,
 which is present since v2.1.0.
 
-Please, note that memory hotunplug is not supported yet. This means
-that you're able to add memory, but you're not able to remove it.
-Also, proper guest support is required for memory hotplug to work.
+And, proper guest support is required for memory hotplug to work.
 
 Basic RAM hotplug
 -----------------
@@ -74,3 +72,21 @@ comes from regular RAM, 1GB is a 1GB hugepage page and 256MB 
is from
    -device pc-dimm,id=dimm1,memdev=mem1 \
    -object memory-backend-file,id=mem2,size=256M,mem-path=/mnt/hugepages-2MB \
    -device pc-dimm,id=dimm2,memdev=mem2
+
+
+QEMU memory hot unplug
+======================
+This part explains how to use the memory hot unplug feature in QEMU.
+
+In order to be able to hot unplug pc-dimm device, QEMU has to be told the id
+of pc-dimm device. The id was assigned when you hot plugged memory.
+
+One monitor command is used to hot unplug memory:
+
+ - "device_del": deletes a front-end pc-dimm device
+
+For example, assuming that the pc-dimm device with id "dimm1" was hotplugged
+into the guest, the following command deletes the pc-dimm device from the
+guest.
+
+  (qemu) device_del dimm1
diff --git a/docs/specs/acpi_mem_hotplug.txt b/docs/specs/acpi_mem_hotplug.txt
index 1290994..a88b286 100644
--- a/docs/specs/acpi_mem_hotplug.txt
+++ b/docs/specs/acpi_mem_hotplug.txt
@@ -2,7 +2,7 @@ QEMU<->ACPI BIOS memory hotplug interface
 --------------------------------------
 
 ACPI BIOS GPE.3 handler is dedicated for notifying OS about memory hot-add
-events.
+and hot-remove events.
 
 Memory hot-plug interface (IO port 0xa00-0xa17, 1-4 byte access):
 ---------------------------------------------------------------
@@ -42,3 +42,17 @@ Selecting memory device slot beyond present range has no 
effect on platform:
      ignored
    - read accesses to memory hot-plug registers not documented above return
      all bits set to 1.
+
+Memory hot remove process diagram:
+----------------------------------
+Memory hot unplug is rather complicated multi-stage process, it is asynchronous
+procedures. The follwoing diagram describes memory hot unplug process.
+
+             QEMU             |             Guest OS
+-------------------------------------------------------------------------------
+     unplug request cb ->     |
+                              |  OSPM processes ejection request
+                              |  <- OSPM clears device remove event
+    clear remove event ->     |
+                              |  <- OSPM issues _EJ0 and initiates device eject
+  unplug cb (eject device)    |
-- 
1.9.3